This invention relates to vascular repair devices, and in particular to intravascular stents, which are adapted to be implanted into a patient's body lumen, such as a blood vessel or coronary artery, to maintain the patency thereof. Stents are particularly useful in the treatment of atherosclerotic stenosis in arteries and blood vessels.
Stents are particularly useful in the treatment and repair of blood vessels after a stenosis has been compressed by percutaneous transluminal coronary angioplasty (PTCA), percutaneous transluminal angioplasty (PTA), or removed by atherectomy or other means, to help improve the results of the procedure and reduce the possibility of restenosis. Stents also can be used to provide primary compression to a stenosis in cases in which no initial PTCA or PTA procedure is performed. While stents are most often used in the procedures mentioned above, they also can be implanted on another body lumen such as the carotid arteries, peripheral vessels, urethra, esophagus and bile duct.
In typical PTCA procedures, a guiding catheter or sheath is percutaneously introduced into the cardiovascular system of a patient through the femoral arteries and advanced through the vasculature until the distal end of the guiding catheter is in the aorta. A guidewire and a dilatation catheter having a balloon on the distal end are introduced through the guiding catheter with the dilatation catheter sliding over the guidewire. The guidewire is first advanced out of the guiding catheter into the patient's vasculature and is directed across the arterial lesion. The dilatation catheter is subsequently advanced over the previously advanced guidewire until the dilatation balloon is properly positioned across the arterial lesion. Once in position across the lesion, the expandable balloon is inflated to a predetermined size with a radiopaque liquid at relatively high pressure to displace the atherosclerotic plaque of the lesion against the inside of the artery wall and thereby dilate the lumen of the artery. The balloon is then deflated to a small profile so that the dilatation catheter can be withdrawn from the patient's vasculature and the blood flow resumed through the dilated artery. As should be appreciated by those skilled in the art, while the above-described procedure is typical, it is not the only method used in angioplasty.
In angioplasty procedures of the kind referenced above, abrupt reclosure may occur or restenosis of the artery may develop over time, which may require another angioplasty procedure, a surgical bypass operation, or some other method of repairing or strengthening the area. To reduce the likelihood of the occurrence of abrupt reclosure and to strengthen the area, a physician can implant an intravascular prosthesis for maintaining vascular patency, commonly known as a stent, inside the artery across the lesion. Stents are generally cylindrically shaped devices which function to hold open and sometimes expand a segment of a blood vessel or other arterial lumen, such as a coronary artery. Stents are usually delivered in a radially compressed condition to the target location and then are deployed into an expanded condition to support the vessel and help maintain it in an open position. The stent is usually crimped tightly onto a delivery catheter and transported in its delivery diameter through the patient's vasculature. The stent is expandable upon application of a controlled force, often through the inflation of the balloon portion of the delivery catheter, which expands the compressed stent to a larger diameter to be left in place within the artery at the target location. The stent also may be of the self-expanding type formed from, for example, shape memory metals or super-elastic nickel-titanium (NiTi) alloys, which will automatically expand from a compressed state when the stent is advanced out of the distal end of the delivery catheter into the body lumen.
The above-described, non-surgical interventional procedures, when successful, avoid the necessity for major surgical operations. Some stents are formed of cylindrical rings which alternate in length between adjacent rings. The variation in cylindrical ring length affects the ability of some of these stents to conform to the natural curvature of a body lumen, such as a curve in a blood vessel. Stent conformability is a function of the sectional rigidity (the resistance to bending of the sectional elements) of a stent design, such as the rigidity of individual cylindrical rings making up the stent. The strut pattern of each of the cylindrical rings includes an undulating pattern of U-shaped portions with the curved portions of the U-shapes being positioned at the first, proximal and second, distal ends of the struts. The U-shapes at the first, proximal end of the cylindrical rings are referred to as peaks while the U-shapes at the second, distal end of the cylindrical rings are referred to as valleys. The peaks and valleys have struts extending therebetween. The rigidity of a cylindrical ring is determined by its geometric features, such as peak/valley radii and strut length. In general, stents with cylindrical rings having longer strut lengths have higher rigidity. Stents with low sectional rigidity generally conform to the body lumens better than stents with high sectional rigidity.
Another source of variation in sectional rigidity is the manner in which connecting elements, such as links, connect the cylindrical rings together. Link patterns which repeat themselves over a certain number of cylindrical rings can often be identified. Some stents have link patterns which repeat themselves over long intervals, thus leading to lower conformability.
Another concern on some stents is that peaks on one cylindrical ring point directly at valleys on an adjacent cylindrical ring in such manner that as the stent traverses and/or is deployed in a curved body lumen, the peaks and valleys on the inside portion of the curve tend to overlap, commonly known as “train wrecking”, while the peaks and valleys on the outside portion of the curve tend to flare out, commonly known as “fish scaling”. The overlap can cause an increase in the biological response to the implanted stent. The overlap may also cause the stent to catch on the balloon. Flaring, on the other hand, is a known contributor to plaque prolapse.
What has been needed is a stent having a reduced amount of variation in the length of the cylindrical rings and shorter intervals for the link patterns to improve conformability of the stent. What has also been needed is a stent that eliminates unsupported peaks and valleys pointing directly at each other or that increase the distance between unsupported peaks and valleys which point directly at each other. The present invention satisfies these needs.